Electromagnetic interference shield

ABSTRACT

An EMI shield that utilizes a waveguide structure in which all or part of the air flow opening has a non-uniform three dimensional shape.

FIELD OF THE INVENTION

[0001] The invention relates generally to electromagnetic interference(EMI) shielding in electronic systems.

BACKGROUND OF THE INVENTION

[0002] The operation of electronic circuitry used in many electronicdevices is often accompanied by unwanted stray electromagneticradiation. Stray electromagnetic radiation or “noise” can interfere withthe performance of surrounding devices. Consequently, it is important toshield electronic devices to reduce electronic noise emanating fromthose devices.

[0003] Redundant arrays of inexpensive or independent storage devices(RAID) are being employed by the mass storage industry to providevariable capacity storage. RAID systems use interconnected disk drivesto achieve the desired capacity of mass storage. With this approach, adisk drive of one capacity may be manufactured and packaged with thesame or different capacity drives to provide the required storagecapacity. RAID systems eliminate the need to manufacture disk drivesindividually designed to meet specific storage requirements. Each diskdrive in a RAID system is usually housed in an individual module forhandling and installation. The modules slide into and out of a largerenclosure that houses the array of disk drives and provides the sockets,plug-ins and other connections for the electrical interconnection of thedrives. Controllers orchestrate the interconnection and control accessto selected disk drives for data reading and writing operations.

[0004] Each module includes a plastic housing and, in most cases, sometype of metal EMI shielding. Metal shielding is often constructed asmetal plates, panels, partial enclosures and the like positioned withinor about the housing. The metal attenuates stray electronic signalsemanating from the module as well as stray signals coming fromsurrounding modules. The degree of attenuation increases with theamount, placement and composition of metal shielding. A closed metalbox, for example, would provide excellent shielding. The housing,however, must also permit sufficient air flow to cool the device duringoperation. Hence, there must be adequate openings in the housing and theshielding to provide the necessary degree of cooling air flow.

[0005] Air flow openings in EMI shields are typically round, square orhexagonal. As the frequencies of the electromagnetic radiation/noise areincreased, the size of the openings are decreased as much as possiblewhile increasing the length of the openings to provide waveguides thatattenuate as much of the electromagnetic radiation as possible whilestill allowing sufficient cooling air flow. The shape of thesewaveguides stays the same across the length of opening. A conventionalwaveguide for EMI shielding, designated by reference number 2, is shownin FIGS. 1 and 2. The range of frequencies of electromagnetic radiationthat will be received into and attenuated by the waveguide is determinedby the shape of the opening.

SUMMARY OF THE INVENTION

[0006] In one embodiment, the invention is directed to an EMI shieldthat utilizes a waveguide having a three dimensionally non-uniformopening. In another embodiment, the invention is directed to an EMIshield that utilizes a waveguide structure in which the entry, andpreferably the exit, is substantially larger than the elongated conduitportion of the waveguide that extends between the entry and the exit. Inanother embodiment of the invention, each waveguide opening ischaracterized by a weak receiving antenna, and preferably a weaktransmitting antenna, and a waveguide operatively connected between thereceiving and transmitting antennas.

DESCRIPTION OF THE DRAWINGS

[0007]FIGS. 1 and 2 are front and side views, respectively, of aconventional waveguide for EMI shielding.

[0008]FIG. 3 is a perspective view of an enclosure for a disk drive orother electronic circuitry in which the front and rear portions of theenclosure are constructed as an EMI shield.

[0009]FIG. 4 is a perspective view of the front of a housing for a groupof individual device modules, such as the disk drive modules used inRAID data storage systems. The electronic device in one or more of themodules may be housed in an enclosure like the one illustrated in FIG.3.

[0010]FIG. 5 is a perspective view of the rear of the housing of FIG. 4.

[0011]FIG. 6 is a close-up perspective view of the rear corner of thedevice module of FIG. 3 showing EMI shielding using waveguidesconstructed according to one embodiment of the present invention.

[0012]FIG. 7 is a detailed perspective view showing one of thewaveguides of FIG. 6.

[0013]FIG. 8 is a plan view of the waveguide of FIG. 7.

[0014]FIG. 9 is a section view taken along the line 9-9 in FIG. 8.

[0015]FIGS. 9A and 9B are section views illustrating alternativeembodiments of a waveguide opening in which the entry, center and exitportions of the opening have comparable cross sectional areas butsubstantially different geometries.

[0016]FIG. 10 is a close-up perspective view of the rear corner of thedevice module of FIG. 3 showing EMI shielding using waveguidesconstructed according to one embodiment of the present invention inwhich the entry portion of the opening is substantially larger than acenter conduit portion of the opening.

[0017]FIG. 11 is a detailed perspective view showing one of thewaveguides of FIG. 10.

[0018]FIG. 12 is a plan view of the waveguide of FIG. 11.

[0019]FIG. 13 is a section view taken along the line 13-13 in FIG. 12.

[0020]FIG. 14 is a detailed perspective view of another embodiment ofthe waveguides of the present invention in which the entry and exit aresubstantially larger than the center conduit portion of the opening.

[0021]FIG. 15 is a plan view of the waveguide of FIG. 14.

[0022]FIG. 16 is a section view taken along the line 16-16 in FIG. 15.

DETAILED DESCRIPTION OF THE INVENTION

[0023]FIG. 3 illustrates an enclosure 10 for a disk drive or otherelectronic circuitry in which the front panel 12 and rear portions 13are constructed as an EMI shield through which cooling air can flow. Amultiplicity of openings 14 are formed along front panel 12 and rearportions 13 of enclosure 10. As described in more detail below, openings14 function as air flow passages for cooling and as waveguides for EMIshielding. Some type of ejector latch 15 is typically used on frontpanel 12 to facilitate the installation and removal of enclosure 10 in agroup housing unit such as the one described below for FIGS. 4 and 5.

[0024] A waveguide is a structure that transmits electromagneticradiation above a certain “cut-off” frequency. If the electromagneticradiation is below the cut-off frequency, then the waveguide rapidlyattenuates the signals. If the electromagnetic radiation is above thecut-off frequency, then the signals pass readily through the waveguide.Waveguide as that term is used in this Specification and in the claimsrefers broadly to any structure forming an opening that will attenuateelectromagnetic radiation.

[0025]FIGS. 4 and 5 illustrate one example of a data storage system 18with which the invention can be used. Referring to FIGS. 4 and 5, datastorage system 18 includes a group of individual device modules 20 and22, such as the disk drive modules used in a RAID data storage systems,housed in a housing 24. FIG. 4 shows the front of housing 24. FIG. 5shows the rear of housing 24. The electronic device in each module 20and 22 is housed in an enclosure like the one illustrated in FIG. 3 inwhich the front panel and rear portions are constructed as an EMIshield. System 18 may also include, for example, power supplies 26 and28, battery back-up units 30 and 32, cooling fan modules 34 and 36 andinput/output modules 38 and 40. Power supplies 26 and 28 provide thenecessary electrical power for system 18. Battery back-up units 30 and32 provide an alternative power source in the event of a failure of oneor more of the power supplies 26 and 28. Fan modules 34 and 36 circulateair through housing 24 to cool the components. The input/output modules38 and 40 enable the system components to communicate with externaldevices. The front panels and other parts of the enclosures for powersupplies 26 and 28 and battery back-ups 30 and 32 might also beconstructed as EMI shields using the structures of the presentinvention.

[0026] The details of one embodiment of the waveguide structure of thepresent invention will now be described with reference to FIGS. 6-9.FIG. 6 is a close-up perspective view of the rear corner of the devicemodule enclosure 10 of FIG. 3. FIGS. 6-9 show one embodiment of an EMIshield in which the waveguide structure that defines openings 14 areused to attenuate electromagnetic radiation while allowing air flowthrough the shield. FIG. 7 is a detailed perspective view of one opening14. FIG. 8 is a plan view of the opening of FIG. 7. FIG. 9 is a crosssection view of the opening taken along the line 9-9 in FIG. 8.

[0027] Referring to FIGS. 6-9, a multiplicity of openings 14 are formedin metal or other conductive material 42. Unlike conventional waveguidesin which the opening is substantially uniform along its length, thewaveguide of the present invention includes an opening defined bynon-uniform three dimensional sidewalls 43. The particular geometry ofthis three dimensional, preferably non-uniform, opening 14 may beselected as necessary or desirable to help optimize performance for anyparticular application. For example, undulations or cavities insidewalls 43 perpendicular to the flow of air through opening 14 can beused to increase the size of opening 14 to permit greater air flow whilestill maintaining the desired level of EMI attenuation. The threedimensional geometry of opening 14 could be selected to createinterference among the electromagnetic waves passing through thewaveguide to improve attenuation without impeding air flow.

[0028] The section views of FIGS. 9A and 9B show alternative embodimentsin which the geometry of opening 14 varies between a non-uniform threedimensional shape and a uniform shape. In FIG. 9A, entry and exitportions 44 and 48 of opening 14 is defined by non-uniform threedimensional sidewalls 43 a and 43 c while a center portion 46 is definedby uniform two dimensional sidewalls 43 b. In FIG. 9B, the entry andexit portions 44 and 48 are defined by uniform two dimensional sidewalls43 b while the center portion 46 is defined by non-uniform threedimensional sidewalls 43 a. FIGS. 9A and 9B illustrate two examples of awaveguide opening 14 in which the entry 44, center 46 and exit 48portions of the opening have comparable cross sectional areas boutsubstantially different geometries.

[0029] While conductive material 42 may be any conductive materialsuitable for EMI shielding, it is expected that plastic or some othertype of moldable or castable material will be used to more easilymanufacture the desired shapes. Non-conductive plastic or other moldablematerial plated with conductive material could also be used.

[0030] Another embodiment of the waveguide structure of the presentinvention is shown in FIGS. 10-13. FIG. 10 is a close-up perspectiveview of the rear corner of the device module enclosure 10 of FIG. 3.FIG. 11 is a detailed perspective view of one opening 14. FIG. 12 is aplan view of the opening of FIG. 11. FIG. 13 is a section view of theopening taken along the line 13-13 in FIG. 12.

[0031] Referring to FIGS. 10-13, a multiplicity of openings 14 areformed in metal or other conductive material 42. Each opening 14 ischaracterized by an entry area 44 and an elongated conduit portion 46.Entry 44 is, at the surface of conductive material 42, larger in crosssectional area than conduit portion 46 and, therefore, the larger entry44 transitions down to the smaller conduit portion 46. Opening up thewaveguide at the receiving point with entry 44 creates an antennastructure that receives electromagnetic radiation emanating from insidethe enclosure. Hence, the shape of entry 44 should be selected tominimize the antenna effect while still achieving the desired air flow.

[0032] In another embodiment of openings 14 shown in FIGS. 14-16,conduit portion 46 extends between entry 44 and a substantially enlargedexit area 48. Exit 48 acts as a transmitting antenna for anyelectromagnetic radiation that survives conduit portion 46. Therefore,like entry 44, exit 48 should be sized and shaped to minimize thisantenna effect.

[0033] The particular geometry of entry 44, conduit 46 and exit 48 maybe selected as necessary or desirable to help optimize performance forany particular application and need not be limited to the circles,rectangles or hexagons typical of conventional waveguides. For entry 44and exit 48, non-uniform shapes, particularly three dimensionallynon-uniform shapes, are expected to have the weakest antenna effect and,therefore, are the presently preferred shapes. Conduit portion 46functions like a conventional waveguide accepting and attenuatingelectromagnetic radiation received through entry 44. The enlarged entry44 and exit 48 effectively increases the size of openings 14, permittinggreater air flow while still achieving the electromagnetic radiationattenuation associated with the smaller diameter conduit portion 46.

[0034] The present invention has been shown and described with referenceto the foregoing exemplary embodiments. Other embodiments are possible.It should be understood, therefore, that the invention is to beconstrued broadly within the scope of the following claims.

What is claimed is:
 1. An electromagnetic interference shield,comprising conductive material having a plurality of elongated openingstherein, each opening being non-uniform in a dimension perpendicular toa longitudinal axis of the opening.
 2. An electromagnetic interferenceshield, comprising conductive material having a plurality of elongatedopenings therein, each opening having a non-uniform three dimensionalshape.
 3. An electromagnetic interference shield, comprising conductivematerial having a plurality of elongated openings therein, each openingincluding a first portion having a non-uniform three dimensional firstshape and a second portion having a second shape different from thefirst shape.
 4. The shield of claim 3, wherein the second shape is auniform two dimensional shape.
 5. The shield of claim 3, wherein thefirst portion comprises an entry to and an exit from the opening and thesecond portion extends between the entry and the exit.
 6. The shield ofclaim 3, wherein the second portion comprises an entry to and an exitfrom the opening and the first portion extends between the entry and theexit.
 7. An electromagnetic interference shield, comprising conductivematerial having a plurality of openings therein, each opening includingan entry and an elongated conduit connected to and extending away fromthe entry, the entry having a first cross sectional area and the conduithaving a second cross sectional area substantially smaller than thefirst cross sectional area.
 8. The shield of claim 7, wherein the entrytapers from the first cross sectional area at an exterior opening downto the second cross sectional area where the entry meets the conduit. 9.The shield of claim 7, wherein each opening further includes an exitconnect to the conduit at a location opposite the entry, the exit havinga third cross sectional area substantially larger than the second crosssectional area.
 10. The shield of claim 9, wherein the entry tapers fromthe first cross sectional area at an exterior opening down to the secondcross sectional area where the entry meets the conduit and the exittapers from the third cross sectional area at an exterior opening downto the second cross sectional area where the exit meets the conduit. 11.An electromagnetic interference shield, comprising conductive materialhaving a plurality of openings, each opening characterized by areceiving antenna and a waveguide operatively connected to the receivingantenna.
 12. The shield of claim 11, wherein the receiving antennacomprises an entry portion of the opening and the waveguide comprises anelongated conduit portion of the opening connected to and extending awayfrom the entry portion of the opening.
 13. The shield of claim 11,further comprising a transmitting antenna operatively connected to thewaveguide at a location opposite the receiving antenna.
 14. The shieldof claim 13, wherein the receiving antenna comprises an entry portion ofthe opening, the transmitting antenna comprises an exit portion of theopening and the waveguide comprises an elongated conduit portion of theopening connected between the entry and the exit.
 15. An electromagneticinterference shielded electronic module, comprising: an electronicdevice capable of generating electromagnetic radiation; and a housing atleast partially enclosing the electronic device, the housing having aplurality of walls at least one of which comprises a conductive materialhaving a plurality of openings therein, each opening having anon-uniform three dimensional shape.
 16. An electromagnetic interferenceshielded electronic module, comprising: an electronic device capable ofgenerating electromagnetic radiation; and a housing at least partiallyenclosing the electronic device, the housing having a plurality of wallsat least one of which comprises a conductive material having a pluralityof openings therein, each opening including an entry and an elongatedconduit connected to and extending away from the entry area, the entryhaving a first cross sectional area and the conduit having a secondcross sectional area substantially smaller than the first crosssectional area.
 17. The module of claim 16, wherein each opening furtherincludes an exit connected to the conduit at a location opposite theentry, the exit having a third cross sectional area substantially largerthan the second cross sectional area.